1. Field of the invention
The present invention relates to an ultrasound sensor used to measure distance, and more particularly to a sensor for determining and indicating distances between vehicles and obstacles at close range using ultrasound techniques, wherein the sensor is able to generate a precise detecting area so as to avoid false activation of the sensor.
2. Description of related art
With reference to FIG. 8, a conventional ultrasound sensor (80) is securely mounted on a rear portion of a vehicle (90), generally at the center of the vehicle (90). It is well know in the art that the sensor (80) comprises a piezoelectric ceramic to generate ultrasound signal beams and the scope of such ultrasound signal beams radiated is substantially a circular form. When the ultrasound signal beams reflected from an obstacle are received by the sensor (80), the sensor (80) is able to measure the distance between the vehicle (90) and the obstacle according to the time interval of the emitted and reflected ultrasound signal beams.
The scope shape defined by the ultrasound signal beams has always been an issue point of the ultrasound sensor improvement. As the foregoing mentioned sensor (80) has a circular form detecting scope, when a lower periphery of the detecting scope reaches the ground, the ultrasound signals are reflected and such a reflection will falsely warn the driver that the vehicle (90) is approaching an obstacle.
With reference to FIG. 9, a conventional sensor mainly comprises a housing (70) with a cylindrical chamber (71) and a piezoelectric ceramic element (72). The chamber (71) receives and seals the piezoelectric ceramic element (72) therein, and the inner diameter of the chamber (71) determines the detecting scope of the ultrasound signals. The smaller the inner diameter of the chamber (71) is, the larger detecting scope is formed (as shown in FIG. 8). On the contrary, the larger the inner diameter of the circular chamber (71) is, the smaller detecting scope is formed (as shown in FIGS. 10A and 10B). However, such a small detecting scope is not able to cover the entire cross sectional area of the vehicle.
For the purpose of overcoming the aforementioned problems, another kind of sensor is disclosed. Such a sensor has an elliptical detecting scope (as shown in FIGS. 11A and 11B). Although the sensitivity of this sensor is better than the earlier cited art, the lower periphery of the elliptical detecting scope is still too close to the ground. Thus the possibility to generate a false warning message still can not be completely avoided.
To overcome the aforementioned problems, the invention provides an ultrasound sensor having a shape that is able to emit signals covering the entire cross sectional area of the vehicle without initiating a false alarm.
The primary objective of the present invention is to provide an ultrasound sensor having a shape to eliminate the possibility of activating a false alarm and to effectively alert the driver that the vehicle is approaching an obstacle.
To achieve the objective of the invention, the ultrasound sensor has a housing defining therein a substantially tapered rectangle chamber, a piezoelectric ceramic element received in the tapered rectangle chamber, and multiple isolating layers received in the tapered rectangle chamber on top of the piezoelectric ceramic element. The isolating layers comprise a silicon rubber layer, a cork layer and a felt layer.
Further objectives and advantages of the present invention will become apparent from a careful reading of the detailed description provided hereinafter, with appropriate reference to the accompanying drawings.